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Avalanche Forecast

Archived

Apr 5th, 2022–Apr 6th, 2022

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Sea To Sky.

The recent storm snow is expected to remain reactive to human triggering, especially in wind-loaded terrain. With extended sun exposure on Wednesday, any unconsolidated storm snow may settle into a more cohesive slab and become increasingly reactive. 

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to the limited number of field observations.

Weather Forecast

A ridge of high pressure brings sunny conditions for Wednesday morning but cloud from a storm system impacting the north coast is expected to spill into the region in the late afternoon. 

Tuesday Night: Mainly clear, light variable wind, freezing level low around 500 m. 

Wednesday: Mainly sunny with increasing cloud cover in the afternoon, light to moderate SW wind, freezing level high around 1700 m.

Thursday: Mainly cloudy with sunny breaks, light to moderate SW wind, freezing level high near 2500 m.

Thursday night and Friday: Precipitation 30-50 mm, sunny breaks in the afternoon, moderate to strong SW wind, freezing level falling to around 1400 m. 

Avalanche Summary

An early report from Tuesday includes several size 1-2 explosive-triggered storm slabs and a remotely-triggered size 2 storm slab which was triggered from 2 m away. 

On Monday, evidence of a recent natural avalanche cycle was reported which had occurred during the storm. Ski cutting and explosives were triggering storm slabs up to size 2, some of which were failing on the melt-freeze crust below the storm snow and some of which were failing on interfaces within the storm snow. Of the avalanches which failed on the crust, many were in the 50-60 cm thickness range in sheltered terrain and up to 100 cm thick in wind loaded terrain. A couple of the avalanches were remotely triggered from a short distance away. 

Snowpack Summary

The recent storm produced 60-80 cm of new snow in the Whistler area. This storm snow has buried a firm crust which extends to mountain top on solar aspects and to around 2200 m on northerly aspects. Strong to extreme southwest wind has redistributed the new storm snow in exposed, high elevation terrain forming wind slabs up to 150 cm thick and developing large cornices. Windward slopes have been scoured down to the crust and the alpine snow surface is expected to be highly variable. 

The middle and lower snowpack are generally strong and well bonded. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.